1. Field of the Invention
The present invention is concerned with a cellular form of solvent refined coal, hereinafter denominated "SRC", and to methods for making such coal.
The invention is based on the unobvious and unpredictable discovery that numerous interconnecting or closed cells can be introduced throughout a mass of solvent refined coal so as to transform it into a two-phase, gas-solid composition of matter in which the solid is a continuous phase.
2. State of the Art
Many natural materials are porous, such as certain gem stones and minerals, but appear to be continous solids because their pores are minute and widely spaced and therefore constitute a very small fraction of the volume of the material. These materials are not generally considered to be cellular in nature. Some natural materials which are cellular in nature include sponges and wood.
Synthetic cellular solid materials are also known. Rubber, plastic, glass, sulfur, metal, and vitreous carbon are examples of materials which have been produced in cellular form. These reticulated gas-solid system are often called foams because they are generated by introducing a gas in the material to be foamed while it is a plastic mass. Agents added to produce a gas are known in the art as blowing agents. However, foams or cellular forms of materials can be obtained by various other methods such as sintering particles together; leaching out solid materials, such as salts, from insoluble continuous phases; mechanically dispersing a quantity of gas into a fluid plastic phase; and dispersing small cellular particles or microballons. All these methods are applicable to SRC and various techniques such as introducing activators, surfactants, and nucleating agents, lowering external pressure, and closely controlling temperature are suitable.
The conditions and methods used to produce cellular SRC depend on economics, environmental considerations, the use of the product, and the properties of the SRC. The method, agents added, temperature, time, pressure, concentrations of additives, etc. to produce cellular SRC give different degrees of density reduction, determine whether the cells are open (interconnecting) or closed, and affect the size, shape, and distribution of cells.
Most of the technology for producing synthetic cellular materials has been in the area of using blowing agents added to materials which are fluid plastic masses at temperatures well below the temperatures where at least some solvent refined coals are fluid. Thus many blowing agents are not suitable for raw solvent refined coal because their gas generation is usually too rapid at temperatures where SRC can be foamed.